前景背景图叠加

 backgroundImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"StarsBackground.png"]];

    backgroundImageView.contentMode = UIViewContentModeLeft;

    [self addSubview:backgroundImageView];

    

    foregroundImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"StarsForeground.png"]];

    foregroundImageView.contentMode = UIViewContentModeLeft;

    foregroundImageView.clipsToBounds = YES;

    [self addSubview:foregroundImageView];